'Small-mindedness that sensed a bigger picture': Mary Whitehouse in 1985. Photograph: E Hamilton West for the Guardian

Almost two decades before Margaret Thatcher became liberal Britain's No1 hate figure there was another woman with firm convictions and an even firmer hairdo who inspired almost as much progressive revulsion. For much of the 60s and 70s, and on into the 80s and even 90s, Mary Whitehouse managed to get up the noses of everyone from pornographers to pop singers.

Dramatists poked fun at her, a hardcore magazine and a comedy sketch show were mockingly named after her and Roger Waters denounced her in Pink Floyd's Pigs as a "house proud town mouse… all tight lips and cold feet". What was it about this housewife and former art teacher from Wolverhampton that got everyone so worked up? An evangelical Christian and self-styled moral crusader, she set out to stem what she saw as the polluted tide of the permissive society, particularly on television, and most specifically on the BBC.

She wrote her first letter of complaint to the BBC in 1963, the year Philip Larkin said that sex was invented. In 1964 she launched the Clean Up TV campaign and in 1965 the National Viewers' and Listeners' Association – a sort of middle England version of the Saudis' Committee for the Promotion of Virtue and Prevention of Vice. Almost nothing appeared to escape her condemnation. Tom and Jerry, Nationwide, documentaries about the Nazis, Whitehouse complained about them all. Alf Garnett from Till Death Us Do Part and the playwright Dennis Potter were guaranteed to make her reach for her letter writing pad.

Without having seen the play, she was jubilant at the BBC's decision in 1976 not to screen Potter's Brimstone and Treacle. "While it is difficult to pre-judge a programme," she wrote to the director general Alasdair Milne, "I can only assume that Brimstone and Treacle was more offensive than Tuesday night's Dennis Potter play Double Dare. In that case, it must indeed be bad."

Throughout the 1960s her protests were largely ignored at the corporation on the instruction of the then DG, Hugh Greene. Once Greene departed she began to get a foot-hold. And although she would remain the target of ridicule, she knew how to parlay her position into one of greater influence. Ben Thompson, who has edited her letters, does not underestimate this influence. "From feminist anti-porn campaigns," he writes, "to UK Uncut, and the Taliban and Mumsnet, Mary Whitehouse's monuments are all around us."

The Taliban does seem a stretch. Did Mullah Omar study Whitehouse's notorious blasphemy case against The Romans in Britain before he laid waste to infidels and heretics in Afghanistan? Thompson, alas, doesn't say.

Yet Thompson is on to something. While Whitehouse remained unwavering in her position, the ground around her shifted. When she started out in the 1960s a libertarian idealism suffused the arts and was making headway in society at large. Each new advance against censorship was seen as an unproblematic triumph over oppression. Then gradually some enlightened attitudes edged towards Whitehouse on issues like the commercial sexualisation of children and the sexual exploitation of women. As Thompson notes, although Whitehouse was a true blue Tory, her view of the sex industry shared common ground with Marxist economic critiques. Hers was always the kind of small-mindedness that sensed a bigger picture. If she were alive today she would no doubt see the Jimmy Savile saga, and the panic it has unleashed at the BBC, as a vindication of her warnings.

A further irony of history is that many of those who were prepared to damn this archetypal petty bourgeois busybody in the most venomous terms when she objected to attacks on Christianity were nowhere to be seen or heard during the religious backlash against the Danish cartoons that depicted the prophet Muhammad.

Which raises the intriguing question of whether Whitehouse was loathed for her piety or her identity, the strength of her opinions or the mildness of her methods. The pen may be mightier than the sword but you can't behead anyone with a Biro. Perhaps Whitehouse would have been taken more seriously by her liberal antagonists if her supporters had offered a plausible violent threat.

What is clear is that religious cranks have gained a great deal of wary respect in recent years and, for all her genteel presentation, Whitehouse was a religious crank. She started out in the evangelical spiritual movement Moral Re-Armament and went on to wage a prolonged war against freedom of expression. She knew what was best for society because she knew what God wanted for society. Had conviction been the extent of her weaponry she would have been no more than the epistolary equivalent of a sandwich-board eccentric. But she also had persistence and an instinctive understanding of media mechanics. Thompson is strong on her tactical nous. "One of Mary Whitehouse's favourite tricks," he writes, "was to refer neutrally to 'controversies' she herself had generated as if they were simply historical facts of which all must take cognisance."

She also knew that the media craves characters. She swiftly became Mary Whitehouse within inverted commas – a position to which her numerous chat-show appearances and six-volume autobiography paid handsome testimony. Her letters, however, are less than riveting. They offer many examples of her calculating nature but few clues as to why she struck fear into the hearts of television executives. Despite the odd flash of wit, they are rather tiresome, as letters of complaint — unless you are the complainant – tend to be.

Far more revealing are the mandarin replies from BBC high-ups and politicians, which often betray a disagreeable mixture of managerial anxiety and patrician disdain.

Thompson is more sympathetic. He respects Whitehouse as a cultural phenomenon but is also archly drawn to her value as a social joke. Yet as he reminds us, it's she who has had the last laugh. For the spirit of this patron saint of orchestrated outrage lives on in drummed-up internet campaigns and Twitterstorms and every righteous complaint ever left in an online comment box.

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